Building a new bass rig - need reccomendations!

[johnallg]

Very basically (bass-ically?!) a ported cab will extend lower in freq with the same driver as it would in a sealed cab. It also will tend to "fart" at the box's tuned frequency if it is overloaded at that frequency. I haven't been able to cause that to happen with my 410HLF - with CAD design, it is less frequent than in the old days.

So in short, you will get a deeper bass sound out of a ported cab.

[jps]

It also weighs 43 kg, about 95 lbs.!!! More than my Ampeg 410HLF!

I thought the 410HLF was more like 110 lbs.

[johnallg]

I just had to look - it IS 110lbs. No wonder my back protests!!

[rictified]

Very basically (bass-ically?!) a ported cab will extend lower in freq with the same driver as it would in a sealed cab. It also will tend to "fart" at the box's tuned frequency if it is overloaded at that frequency. I haven't been able to cause that to happen with my 410HLF - with CAD design, it is less frequent than in the old days.

So in short, you will get a deeper bass sound out of a ported cab.

A speaker will not work much below it's resonant frequency no matter what kind of cab it is in. A sealed cab will go deeper than a ported cab as ported cabs drop off like a rock below the tuned port's frequency, a sealed cab has no cut off point except for the speaker(s) resonant frequency which is why speakers with a very low resonant frequency are used in sealed cabs, they just get progressively softer and softer. Decent ported cabs shouldn't fart at the tuned frequency as 99.9% of tuned port cabs are tuned higher than the resonant frequency of the speakers in it. This is done so there isn't a large hump at the resonant frequency. They will fart if you try to go lower than the port's resonant frequency as the speaker is not loaded below it. Ported cabs are much harder to design than sealed cabs which are much more forgiving. A Ported cab's virtue is that it is more efficient than a sealed cab, which is why most small cabs are ported in some way. A sealed cab can take more power, has a much more gradual dropoff, and sounds and plays much tighter, a ported cab is looser and louder basically although the new ones are pretty good. There are tradeoffs with each. Ampeg makes both, the classic sealed cab is the SVT cab and the classic ported cab is the Ampeg B-15N portaflex. A ported cab takes the speaker's out of phase back wave and puts it in phase with the front wave which is why they are louder, a sealed cab eliminates the out of phase back wave altogether which is why they are less efficient, there is no abrupt drop off point as in a ported cab.

[johnallg]

But the same driver in a ported cab will stay louder lower than the same driver in a sealed cab. I just ran 3 different driver simulations and all three showed that. For a 12" driver I have, ported it is -3dB at 21.7Hz and for sealed it is -3dB at 37.4Hz. SPL at 40Hz is 3dB higher for the ported over the sealed. It isn't until 12Hz that the sealed gets louder than the ported.

Fs on this driver is 20Hz.

[rictified]

What frequency was the port set for John?

[rictified]

You can do anything on a computer John I believe a cab that used a 20 Kc resonant frequency speaker (never heard of that, would be too flabby for a ported cab) and was ported for maybe 30 Kc which is what I assume you would do as you can't port a cab at the speaker's resonant frequency for the above reasons would either be extremely large or extremely inefficient losing the advantage of a ported cab. There are giant EAW bottoms which I do think go way down there and sound great but you need a crane to move them.. Where does your 410 HLF drop off?

[johnallg]

Port was set to 21.49 Hz. Fs of the driver was 20 Hertz, not 20 kilohertz. Box volume was 8.312 cu ft. Vent was 4" diameter and 5.79" long. It was in a transmission line 3 way speaker I built for many years, and sounded very good.

Ampeg doesn't give you much - they say -3dB at 48hz, and -10db at 28 hz.

[sloop_john_b]

Sheesh, this is all way over my head.

Well, I know i'm gonna go for the Markbass LMKII head and the Markbass 4x10 ported cabinet, just need to scrounge up the extra dough first. I just love the fact that this setup will be louder than my B200R and weigh less in total too!

[jps]

Good move, John. Maybe when you get to us elders ages your back won't feel like ours!

[rictified]

Port was set to 21.49 Hz. Fs of the driver was 20 Hertz, not 20 kilohertz. Box volume was 8.312 cu ft. Vent was 4" diameter and 5.79" long. It was in a transmission line 3 way speaker I built for many years, and sounded very good.

Ampeg doesn't give you much - they say -3dB at 48hz, and -10db at 28 hz.

20 Kc driver! I'm too used to RF. You wouldn't be able to use a cab like that to play a bass through though. Transmission line speakers are not considered ported cabs anyway, at least not in the conventional sense. Those figures for your Ampeg sound about right for a ported bass cab to me, they can't really make them go any lower without either making them very inefficient or making them huge.
SVT cabs are ( if I remember right) down 3db at 40 hz.

[johnallg]

Bob, I figured it was a typo! No, you wouldn't play bass guitar through a cab like that, I was just showing the relationships between the two cab styles.

I did design a cab for two of those drivers and gathered the parts. I stumbled finding 3/4" baltic birch or any dense layered plywood to build it with. I plan to try again this winter. I want it for at home in the practice room so I don't have to haul the 410HLF all the time.

Hey John, great choice! I sure wish our GC, or even the one 60 miles north, carried the Mark Bass equipment. I'd really like to give it a listen.try. I have to go all the way over to Canton MI on the east side of the state for the nearest store.

Oh, and very nice avatar!

[rictified]

[quote="johnallg"]Bob, I figured it was a typo! No, you wouldn't play bass guitar through a cab like that, I was just showing the relationships between the two cab styles.

The way I read it John was that you were claiming it was ported cab used to bolster your contention that ported cabs could go lower than sealed cabs, transmission ine cabs and ported cabs are completely different designs. In reality any ported cab that was ported at 20 Kc with a 21 Kc driver would either be way to big to move or would be very inefficient and would be boomy as hell at the port frequncy although there is not much that goes that low. As it stands practically if you want clear flat uncolored bottom a sealed cab is the way to go.

I did design a cab for two of those drivers and gathered the parts. I stumbled finding 3/4" baltic birch or any dense layered plywood to build it with. I plan to try again this winter. I want it for at home in the practice room so I don't have to haul the 410HLF all the time.

Let me know how it sounds when you get it finished John. I once used a (JBL?) single 15" cab that was ported low although not anywhere near 20 Hz and it was way too low to use with a bass guitar, was good for the bottom octave only if I remember right, was nice for music though. It needed a low mid cab along with it which I don't like. The reason I like the SVT cabs so much is that they are fairly flat all the way down to 40 Hz, very few ported cabs are unless they are small and use a 1000 watt amp.
quote]

[johnallg]

Bob, I was using that as a "fer instance" that ported cabs do go lower than sealed, same driver. And the cab I used for my example was a 6 cu. ft. cab design.

The cab I designed for two of these drivers is a sealed cabinet, because of two reasons: I wanted a smaller cabinet, and more importantly, I agree with you - "As it stands practically if you want clear flat uncolored bottom a sealed cab is the way to go."

It ended up with a 6.346 cu. ft. internal volume and accounting for bracing and driver volume, ended up 24W x 37.5H x 15D. It will be -3dZB at 37.94hz and -10dB at 23.2hz with 300W power driving it and measured at 1 meter. Maybe I should take up 5 string basses.....

[jps]

Biscuti, are you interested in a nice combo amp? Check out my post in The Others about my SWR Baby Blue II amp.